The present invention relates to a method for preparing a perfluoroalkyl group-containing organopolysiloxane, and more particularly, to a method for the simple synthesis of an organopolysiloxane containing a perfluoroalkyl group having at least 4 carbon atoms and having a high degree of polymerization.
In the prior art, several methods are well known for preparing perfluoroalkyl group-containing organopolysiloxanes. One known method involves reacting a perfluoroalkyl group-containing alkenyl compound with a hydrogen containing chlorosilane in the presence of a platinum catalyst to synthesize a perfluoroalkyl group-containing chlorosilane, followed by hydrolysis and condensation as disclosed in Japanese Patent Publication Nos. 2694/1959 and 5593/1959. Another method is by co-hydrolysis of a perfluoroalkyl group-containing chlorosilane and a diorganodichlorosilane to form a copolymer of perfluoroalkyl group-containing siloxane and organosiloxane units as disclosed in Japanese Patent Publication Nos. 24743/1970. However, it is difficult to prepare organopolysiloxanes having a high molecular weight using these methods.
A still further method is known from U.S. Pat. No. 3,002,951,wherein a perfluoroalkyl group-containing chlorosilane is hydrolyzed to form a cyclic diorganosiloxane which is then polymerized in the presence of an alkali metal or alkali metal silanolate. However, it is difficult to synthesize organopolysiloxanes containing a perfluoroalkyl group having at least 4 carbon atoms using this method.
For the preparation of polymers having a high molecular weight, U.S. Patent No. 4,317,899 discloses method for polymerizing trifluoropropyl group-containing cyclic siloxane and a compound of the general formula: EQU HO-[-Si(R') (R'')O-].sub.s -H
wherein R' is an alkyl or phenyl group, R" is CH.sub.3 CH.sub.2 CH.sub.2, group, and letter s is a number having a value of 2 to 50 in the presence of a strong base. This method is limited to the preparation of trifluoropropyl group-containing organo polysiloxanes.
As described above, it was difficult in the prior art to prepare perfluoroalkyl group-containing organopolysiloxanes having a high molecular weight.